Managing Stripe Rust in Pacific Northwest Winter Wheat.

In the last several years the predominant stripe rust races across the Pacific Northwest have changed.  The new stripe rust races are more aggressive and tend to cause more damage to the commonly grown wheat varieties in the region.  In addition the new races appear to be less sensitive to cold and warm temperatures.  This allows them to survive through a mild winter and infect the wheat crop earlier as well as continue to infect the wheat crop late into the season.  Thus, these new stripe rust races have the ability to significantly reduce wheat production if not controlled.  In 2011, grain yield was reduced by ~80-90% in susceptible varieties and 20-40% in moderately resistant varieties when stripe rust was not controlled through the use of fungicides.  While breeding programs are moving rapidly to introduce more resistant wheat varieties, it is likely that growers will need to rely on fungicide applications to control stripe rust in the coming years.  A coordinated project across Oregon, Idaho, and Washington was established in the fall of 2011 to provide growers with improved stripe rust management recommendations.  Project objectives include the evaluation of fungicide efficacy for control of stripe rust on susceptible, moderately susceptible, and resistant winter wheat varieties; the determination of the optimum timing of fungicide application(s) based on three growth stages, jointing, flag leaf emergence, and heading; and the effect of fungicide class on the control of stripe rust.  Study sites were located throughout the tri-state region to capture a range of growing environments.  Treatments were arranged in a split-plot design with four replications.  Whole plots consisted of ten fungicide application timings and/or products.  Subplots consisted of three wheat varieties. Prior to each fungicide application, treatments were evaluated for visual disease symptoms on a 1-100 scale (% leaf infection).  At maturity, plots were harvested using a small plot combine and measurements of grain yield, test weight, and grain protein content obtained.  Data was analyzed using SAS software and means separated.